Quercetin supplements may have exercise benefits: RCT

Supplementation with quercetin, a polyphenol found in food like apples and onions, may boost antioxidant defenses and protect against exercise-induced oxidative damage, says a new study from Italy.

Two weeks of supplementation with one gram per day of quercetin was associated with a better response to the oxidative environment produced by eccentric exercise, compared with placebo, report scientists from the Foro Italico University of Rome.

“Our study provides evidences that quercetin supplementation, prior to and after a strenuous eccentric exercise, makes erythrocytes [red blood cells] more able to cope with oxidative insult,” ​they wrote in Nutrition Research​. “This protective effect ensures an efficient oxygen delivery to the tissues, otherwise compromised by the deleterious effects of the increase in free radicals produced after eccentric exercise. ​

“Altogether, our data may be of benefit for professionals involved in sport nutrition to widen dietary strategies applied to training.”​

Study details​

The Rome-based scientists recruited 14 men with an average age of 25.5 to participate in their controlled, randomized, crossover, intervention trial. The men were randomly assigned to consumer either quercetin supplements or placebo for two weeks before and after a bout of eccentric exercise to eccentric induced muscle damage (EIMD). This was followed by a three-week “washout” period before the men crossed-over to the other intervention.

Commenting on the doses used, the researchers explained that for healthy people, “it has been demonstrated that a dose of 500 mg quercetin aglycone supplied in tablets, was comparable with the quercetin present in approximately 100 g of fresh red onion as assessed by urinary excretion. Hence, we have chosen to conduct the present investigation over a period of two weeks with two daily intake of quercetin (500 mg every 12 hours) based on both real food composition and the bioavailability test already reported in healthy volunteers.”​

The results showed that quercetin consumption was associated with significant reduction in levels of lipid peroxidation in red blood cells, as well as TBARs (thiobarbituric acid reactive substances) in plasma, which is a measure of oxidative damage.

“After a single bout of eccentric exercise, quercetin supplementation improved redox status as assessed by reduced/oxidized glutathione ratio analysis and reduced TBARs levels both in erythrocytes and plasma,”​ wrote the reearchers.

“[O]ur study provides evidences that chronic quercetin supplementation has antioxidant potential prior to and after a strenuous eccentric exercise thus making the erythrocytes capable to better cope with an oxidative insult,” ​they concluded.